<?php
    /**
     * Created by PhpStorm.
     * User: huangzhongwei
     * Date: 2018/9/13
     * Time: 13:42
     */

    /**
     * 对微信小程序用户加密数据的解密
     */

    namespace app\api\service;

    use app\lib\exception\SuccessMessage;
    use app\lib\exception\WeChatException;
    use think\exception\ThrowableError;


    class WXBizDataCrypt
    {

        private $appid;
        private $sessionKey;

        /**
         * 构造函数
         * @param $sessionKey string 用户在小程序登录后获取的会话密钥
         * @param $appid string 小程序的appid
         */
        public function __construct( $appid, $sessionKey)
        {
            $this->sessionKey = $sessionKey;
            $this->appid = $appid;
        }


        /**
         * 检验数据的真实性，并且获取解密后的明文.
         * @param $encryptedData string 加密的用户数据
         * @param $iv string 与用户数据一同返回的初始向量
         * @param $data string 解密后的原文
         *
         * @return int 成功0，失败返回对应的错误码
         */
        public function decryptData( $encryptedData, $iv, &$data )
        {
            if (strlen($this->sessionKey) != 24) {
                throw new WeChatException([
                    'msg'=>'sessionKey格式错误'
                                          ]);
            }
            $aesKey=base64_decode($this->sessionKey);


            if (strlen($iv) != 24) {
                throw new WeChatException(
                    [
                        'msg'=>'iv格式错误'
                    ]
                );
            }
            $aesIV=base64_decode($iv);

            $aesCipher=base64_decode($encryptedData);

            $result=openssl_decrypt( $aesCipher, "AES-128-CBC", $aesKey, 1, $aesIV);

            $dataObj=json_decode( $result,true );
            if( $dataObj  == NULL )
            {
                throw new WeChatException();
            }
            if( $dataObj['watermark']['appid'] != $this->appid )
            {
                throw new WeChatException([
                                              'msg'=>'appid错误'
                                          ]);
            }
            $data = $result;
            return $data;
        }

    }